Download Intro Cell-Cell Communication

Cell To Cell Communication
Local and Long-Distance Signaling
• Cells in a multicellular organism communicate by
chemical messengers
• Animal and plant cells have cell junctions that
directly connect the cytoplasm of adjacent cells
• In local signaling, animal cells may communicate
by direct contact, or cell-cell recognition
Plasma membranes
Gap junctions
between animal cells
(a) Cell junctions
(b) Cell-cell recognition
Plasmodesmata
between plant cells
• Animcal cells communicate using local
regulators, messenger molecules that travel only
short distances
• In long-distance signaling, plants and animals use
chemicals called hormones
• The ability of a cell to respond to a signal depends
on whether or not it has a receptor specific to that
signal
Figure 11.5
Local signaling
Long-distance signaling
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid.
(a) Paracrine signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter.
Endocrine cell
Neurotransmitter
diffuses across
synapse.
Secretory
vesicle
Target cell
is stimulated.
Blood
vessel
Hormone travels
in bloodstream.
Target cell
specifically
binds
hormone.
(b) Synaptic signaling
(c) Endocrine (hormonal) signaling
Figure 11.5a
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter.
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid.
(a) Paracrine signaling
Neurotransmitter
diffuses across
synapse.
Secretory
vesicle
Target cell
is stimulated.
(b) Synaptic signaling
Figure 11.5b
Long-distance signaling
Endocrine cell
Blood
vessel
Hormone travels
in bloodstream.
Target cell
specifically
binds
hormone.
(c) Endocrine (hormonal) signaling
The Three Stages of Cell Signaling: Preview
• Cells receiving signals went through three
processes
– Reception
– Transduction
– Response
Figure 11.6-1
EXTRACELLULAR
FLUID
1 Reception
Receptor
Signaling
molecule
CYTOPLASM
Plasma membrane
Figure 11.6-2
EXTRACELLULAR
FLUID
1 Reception
CYTOPLASM
Plasma membrane
2 Transduction
Receptor
Relay molecules in a signal transduction
pathway
Signaling
molecule
Figure 11.6-3
EXTRACELLULAR
FLUID
1 Reception
CYTOPLASM
Plasma membrane
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction
pathway
Signaling
molecule
Reception: A signaling molecule binds to a
receptor protein, causing it to change shape
• The binding between a signal molecule (ligand)
and receptor is highly specific
• A shape change in a receptor is often the initial
transduction of the signal
• Most signal receptors are plasma membrane
proteins
Receptors in the Plasma Membrane
• Most water-soluble signal molecules bind to
specific sites on receptor proteins that span the
plasma membrane
• There are three main types of membrane
receptors
– G protein-coupled receptors
– Receptor tyrosine kinases
– Ion channel receptors
• G-protein-coupled receptor are the largest
family of cell-surface receptors
• A GPCR is a plasma membrane receptor that
works with the help of a G protein
• The G protein acts as an on/off switch: If GDP is
bound to the G protein, the G protein is inactive
Signaling molecule binding site
Segment that
interacts with
G proteins
Figure 11.7b
G protein-coupled
receptor
Plasma
membrane
Activated
receptor
1
Inactive
enzyme
GTP
GDP
GDP
CYTOPLASM
Signaling
molecule
Enzyme
G protein
(inactive)
2
GDP
GTP
Activated
enzyme
GTP
GDP
Pi
3
Cellular response
4
Figure 11.8
2-adrenergic
receptors
Plasma
membrane
Cholesterol
Molecule
resembling
ligand
• Receptor tyrosine kinases (RTKs) are
membrane receptors that attach phosphates to
tyrosines
• A receptor tyrosine kinase can trigger multiple
signal transduction pathways at once
• Abnormal functioning of RTKs is associated with
many types of cancers
Figure 11.7c
Signaling
molecule (ligand)
Ligand-binding site
 helix in the
membrane
Signaling
molecule
Tyrosines
CYTOPLASM
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
1
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Dimer
2
Activated relay
proteins
3
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
6
ATP
Activated tyrosine
kinase regions
(unphosphorylated
dimer)
6 ADP
Fully activated
receptor tyrosine
kinase
(phosphorylated
dimer)
4
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
• A ligand-gated ion channel receptor acts as a
gate when the receptor changes shape
• When a signal molecule binds as a ligand to the
receptor, the gate allows specific ions, such as
Na+ or Ca2+, through a channel in the receptor
Figure 11.7d
1
Signaling
molecule
(ligand)
3
2
Gate
closed
Ions
Plasma
Ligand-gated
membrane
ion channel receptor
Gate closed
Gate
open
Cellular
response
Intracellular Receptors
• Intracellular receptor proteins are found in the
cytosol or nucleus of target cells
• Small or hydrophobic chemical messengers can
readily cross the membrane and activate
receptors
• Examples of hydrophobic messengers are the
steroid and thyroid hormones of animals
• An activated hormone-receptor complex can act
as a transcription factor, turning on specific
genes
Figure 11.9-1
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
DNA
NUCLEUS
CYTOPLASM
Figure 11.9-2
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
NUCLEUS
CYTOPLASM
Figure 11.9-3
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
NUCLEUS
CYTOPLASM
Figure 11.9-4
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
mRNA
NUCLEUS
CYTOPLASM
Figure 11.9-5
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
mRNA
NUCLEUS
CYTOPLASM
New protein
Hormone Responses
Peptide Based Hormones
• Bind to receptors on the
cell membrane
• Do not enter cell (polar)
• Induce a cascading effect
• Amino acids
• 2nd messengers
• Rapid speed of effect
• Temporary effect
• Ex: Insulin, ADH,
calcitonin
Steroid Based Hormones
• Enter the cell (non polar)
• Receptor is in cytosol of
cell or nucleus
• Slower speed of effect
• More permanent effect
• Travel to the nucleus
• Lipids
• Ex: Testosterone,
estrogen